I found this out only recently myself. Also, if you happen to have ENDISWAL, this lets you destroy plants without angering the Earthmother (excluding the magic immune ones, of course).

i love the Earthmother. She's useful if found early (where Stone Skin and Greenblood make a significant difference), useful if found late (plantation + clearance for mana spikes), useful throughout the entire dungeon (mass slow for 5 Piety!), great for converting out (Plantation for easy 100 Piety, great for converting into anyone except Dracul), great for desecration (costs 1 burn salve) and not only gives you IMAWAL, but gives you ways to use it without having to sacrifice Popcorn! It's also very easy to avoid angering her. Oh, and acid casters. Basically, it's very rare that I feel the Earthmother to be a waste an altar spot. If only she weren't so painful to use in the vicious dungeons...

(Obviously the people who've posted in here didn't need me to tell them this... )

A big part of my EM strategy is to spam Vine Form or Greenblood early, specifically to create plants for piety/xp bonuses. We tend to think of her as a post-exploration deity on account of Plantation, but she can be an even bigger piety farm than Binlor on an unexplored map, provided you generate enough plants.

Yeah, I spent FOREVER trying to get her to work on "natural" Vicious dungeons. None of those dungeons have enough space to make it work. It was only the introduction of the Titan Guitar "bug" that made it possible. The Earthmother Healthmonster works at least as well in Naga City as the classical Absolution one, providing you can stand losing the Fireheart for the Guitar.

Funnily enough, EM is my deity of choice a lot of the time. Once you get stuck with an Avatar's Codex in your locker it's incredibly hard to resist just bringing her and it along every time you fell like not thinking much about what preps to take.

Its also rather easy to fall into a pattern of having a guaranteed IMAWAL XP perks on every run.

Personally, EM is my favorite deity when using Warlords. It feels like she's custom tailored for them - Cydestepp+Vineform+Entanglement easily allows you to kill stuff multiple levels higher, and IMAWAL lets you harvest tons of bonus XP Also, global slow = awesome, and its one of the cheapest boons in the game. Piety is also easy to generate with her, and Plantation can be used for either an Clearance spike or conversion.